Ttyjukl

How to make payment on the internet without leaving a money trail?

Can a German sentence have two subjects?

Why Is Death Allowed In the Matrix?

How do I create uniquely male characters?

Email Account under attack (really) - anything I can do?

Work Breakdown with Tikz

Copycat chess is back

Why did the Germans forbid the possession of pet pigeons in Rostov-on-Don in 1941?

Why are 150k or 200k jobs considered good when there are 300k+ births a month?

What exactly is the parasitic white layer that forms after iron parts are treated with ammonia?

Are there any consumables that function as addictive (psychedelic) drugs?

Copenhagen passport control - US citizen

How to report a triplet of septets in NMR tabulation?

Example of a relative pronoun

Shell script can be run only with sh command

DOS, create pipe for stdin/stdout of command.com(or 4dos.com) in C or Batch?

What makes Graph invariants so useful/important?

Can I make popcorn with any corn?

N.B. ligature in Latex

Is Social Media Science Fiction?

How is it possible for user's password to be changed after storage was encrypted? (on OS X, Android)

"which" command doesn't work / path of Safari?

A function which translates a sentence to title-case

Is there a familial term for apples and pears?

What is the logic behind how bash tests for true/false?

What is the difference between : and true?What is the builtin `:` used for in Bash?bash script trap for exit and err and logic for differenceWhat is the rationale behind $array not expanding the whole array in ksh and bash?extract columns from TRUE/FALSE matrix based on proportion of TRUE values within the columnExpression evaluates to false in for loop whereas it's true in ifWhy does `source foo && true` exit the script in bash?for loop logic porting from bash to cshBash: how can I run `sudo -n true` in the background without interfering with `read`?What's the purpose of “true” in bash “if sudo true; then”

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}

1

This:

echo $VAR

yields: something

And this:

[[ -z "$VAR" ]]
echo $?

yields: 1

Yet this:

if [[ -z "$TMUX_MAN_PANE" ]]; then
echo 'NEVER PRINTS!'


This screws with my head and I need some kind logical way to think about this before I go insane.

UPDATE

Here's some real code. I can't get this to fucking work for the life of me. Fuck bash. :)

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  tmux list-panes -t $TMUX_MAN_PANE &> /dev/null

  echo $?

  echo $TMUX_MAN_PANE

  [[ -z "$TMUX_MAN_PANE" ]]

  echo $?

  if ! [[ -z "$TMUX_MAN_PANE" ]] && [[ $? ]]; then

    echo luck

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    echo fuck

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}

UPDATE 2: Success

Finally figured it out. Was hvaing a hell of a time getting the status of the first line in the if statement. Had to do some trickery to get the output of the tmux statement in the first line of the if statement. If anyone knows a cleaner way to do this, I'm all ears.

Holy shit, I don't know how people program in Bash. Drives me nuts. Sorry for the foul language. I was apeshit. :) Here's the working code:

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  fucker=$(tmux list-panes -t $TMUX_MAN_PANE 2>&1)

  if ! [[ -z "$TMUX_MAN_PANE" ]] && ! [[ $fucker =~ 'find pane' ]]; then

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}



tmux_man_page_close() {

  if [ $TMUX_MAN_PANE ]; then

     tmux kill-pane -t $TMUX_MAN_PANE

  fi

}

bash

share|improve this question

edited 45 mins ago

StevieD

asked 1 hour ago

StevieDStevieD

1679

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Your update does not include enough information. Please (a) include the values of TERM, TMUX, and TMUX_MAN_PANE from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.
  
  – John1024
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
  
  – StevieD
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
  
  – StevieD
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I should just be going this in perl. Fuck this crazy shit.
  
  – StevieD
  54 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Jesus, finally figured it out. Posting solution.
  
  – StevieD
  49 mins ago
  
  
  

  
  
  
  

add a comment | 

1

This:

echo $VAR

yields: something

And this:

[[ -z "$VAR" ]]
echo $?

yields: 1

Yet this:

if [[ -z "$TMUX_MAN_PANE" ]]; then
echo 'NEVER PRINTS!'


This screws with my head and I need some kind logical way to think about this before I go insane.

UPDATE

Here's some real code. I can't get this to fucking work for the life of me. Fuck bash. :)

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  tmux list-panes -t $TMUX_MAN_PANE &> /dev/null

  echo $?

  echo $TMUX_MAN_PANE

  [[ -z "$TMUX_MAN_PANE" ]]

  echo $?

  if ! [[ -z "$TMUX_MAN_PANE" ]] && [[ $? ]]; then

    echo luck

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    echo fuck

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}

UPDATE 2: Success

Finally figured it out. Was hvaing a hell of a time getting the status of the first line in the if statement. Had to do some trickery to get the output of the tmux statement in the first line of the if statement. If anyone knows a cleaner way to do this, I'm all ears.

Holy shit, I don't know how people program in Bash. Drives me nuts. Sorry for the foul language. I was apeshit. :) Here's the working code:

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  fucker=$(tmux list-panes -t $TMUX_MAN_PANE 2>&1)

  if ! [[ -z "$TMUX_MAN_PANE" ]] && ! [[ $fucker =~ 'find pane' ]]; then

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}



tmux_man_page_close() {

  if [ $TMUX_MAN_PANE ]; then

     tmux kill-pane -t $TMUX_MAN_PANE

  fi

}

bash

share|improve this question

edited 45 mins ago

StevieD

asked 1 hour ago

StevieDStevieD

1679

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Your update does not include enough information. Please (a) include the values of TERM, TMUX, and TMUX_MAN_PANE from before the function runs and (b) include the output of the function and then (c) explain how that output differs from what you expect.
  
  – John1024
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It's all a mess. In the first line of the if statement, I just want to know if that command is throwing an error. There is no seemingly rational way to do that. I don't want the output from the command, I want to know if it's throwing an error. That's it.
  
  – StevieD
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  It's showing the command was a success even though it can't find the pane. I see no way to extract the output from that tmux command.
  
  – StevieD
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I should just be going this in perl. Fuck this crazy shit.
  
  – StevieD
  54 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Jesus, finally figured it out. Posting solution.
  
  – StevieD
  49 mins ago
  
  
  

  
  
  
  

add a comment | 

This:

echo $VAR

yields: something

And this:

[[ -z "$VAR" ]]
echo $?

yields: 1

Yet this:

if [[ -z "$TMUX_MAN_PANE" ]]; then
echo 'NEVER PRINTS!'


This screws with my head and I need some kind logical way to think about this before I go insane.

UPDATE

Here's some real code. I can't get this to fucking work for the life of me. Fuck bash. :)

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  tmux list-panes -t $TMUX_MAN_PANE &> /dev/null

  echo $?

  echo $TMUX_MAN_PANE

  [[ -z "$TMUX_MAN_PANE" ]]

  echo $?

  if ! [[ -z "$TMUX_MAN_PANE" ]] && [[ $? ]]; then

    echo luck

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    echo fuck

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}

UPDATE 2: Success

Finally figured it out. Was hvaing a hell of a time getting the status of the first line in the if statement. Had to do some trickery to get the output of the tmux statement in the first line of the if statement. If anyone knows a cleaner way to do this, I'm all ears.

Holy shit, I don't know how people program in Bash. Drives me nuts. Sorry for the foul language. I was apeshit. :) Here's the working code:

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  fucker=$(tmux list-panes -t $TMUX_MAN_PANE 2>&1)

  if ! [[ -z "$TMUX_MAN_PANE" ]] && ! [[ $fucker =~ 'find pane' ]]; then

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}



tmux_man_page_close() {

  if [ $TMUX_MAN_PANE ]; then

     tmux kill-pane -t $TMUX_MAN_PANE

  fi

}

bash

share|improve this question

edited 45 mins ago

StevieD

asked 1 hour ago

StevieDStevieD

1679

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  tmux list-panes -t $TMUX_MAN_PANE &> /dev/null

  echo $?

  echo $TMUX_MAN_PANE

  [[ -z "$TMUX_MAN_PANE" ]]

  echo $?

  if ! [[ -z "$TMUX_MAN_PANE" ]] && [[ $? ]]; then

    echo luck

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    echo fuck

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}

tmux_man_page() {

if [[ "$TERM" =~ 'screen' ]] && [[ -n "$TMUX" ]]; then

  fucker=$(tmux list-panes -t $TMUX_MAN_PANE 2>&1)

  if ! [[ -z "$TMUX_MAN_PANE" ]] && ! [[ $fucker =~ 'find pane' ]]; then

    tmux -q respawn-pane -k -t $TMUX_MAN_PANE man $1

  else

    tmux split-window -vf man $1

    TMUX_MAN_PANE=$(tmux display-message -p "#{pane_id}")

    export TMUX_MAN_PANE

    tmux select-pane -t {last}

  fi

fi

}



tmux_man_page_close() {

  if [ $TMUX_MAN_PANE ]; then

     tmux kill-pane -t $TMUX_MAN_PANE

  fi

}

share|improve this question

edited 45 mins ago

StevieD

asked 1 hour ago

StevieDStevieD

1679

share|improve this question

edited 45 mins ago

StevieD

asked 1 hour ago

StevieDStevieD

1679

asked 1 hour ago

StevieDStevieD

1679

asked 1 hour ago

StevieDStevieD

1679

1 Answer
1

active

oldest

votes

4

The key is that 0 means true and 1 (or any other non-zero value) means false.

In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$VAR" ]] returns code zero (true) if $VAR is empty or one (false) if it is not empty:

$ var=""; [[ -z "$var" ]]; echo $?

0

$ var="NOT EMPTY"; [[ -z "$var" ]]; echo $?

1

In sum, if $VAR is non-empty, then [[ -z "$VAR" ]] is false (returns 1) and the then statement does not execute.

Did you intend for the test to return true if the variable was non-empty? If so, replace -z with -n:

$ var=""; [[ -n "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ -n "$var" ]]; echo $?

0

For brevity, the same test is performed if -n is omitted:

$ var=""; [[ "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ "$var" ]]; echo $?

0

share|improve this answer

edited 1 hour ago

answered 1 hour ago

John1024John1024

48.4k5113128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
  
  – StevieD
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @StevieD Run set -x and then run your code. This will show you how every step is evaluated.
  
  – John1024
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah, shit. Forgot about that setting. I'll try it.
  
  – StevieD
  1 hour ago
  

  
  
  
  

add a comment | 

Your Answer

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "106"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f511129%2fwhat-is-the-logic-behind-how-bash-tests-for-true-false%23new-answer', 'question_page');
}
);

Post as a guest

Name

Email

Required, but never shown

4

The key is that 0 means true and 1 (or any other non-zero value) means false.

In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$VAR" ]] returns code zero (true) if $VAR is empty or one (false) if it is not empty:

$ var=""; [[ -z "$var" ]]; echo $?

0

$ var="NOT EMPTY"; [[ -z "$var" ]]; echo $?

1

In sum, if $VAR is non-empty, then [[ -z "$VAR" ]] is false (returns 1) and the then statement does not execute.

Did you intend for the test to return true if the variable was non-empty? If so, replace -z with -n:

$ var=""; [[ -n "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ -n "$var" ]]; echo $?

0

For brevity, the same test is performed if -n is omitted:

$ var=""; [[ "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ "$var" ]]; echo $?

0

share|improve this answer

edited 1 hour ago

answered 1 hour ago

John1024John1024

48.4k5113128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
  
  – StevieD
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @StevieD Run set -x and then run your code. This will show you how every step is evaluated.
  
  – John1024
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah, shit. Forgot about that setting. I'll try it.
  
  – StevieD
  1 hour ago
  

  
  
  
  

add a comment | 

4

The key is that 0 means true and 1 (or any other non-zero value) means false.

In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$VAR" ]] returns code zero (true) if $VAR is empty or one (false) if it is not empty:

$ var=""; [[ -z "$var" ]]; echo $?

0

$ var="NOT EMPTY"; [[ -z "$var" ]]; echo $?

1

In sum, if $VAR is non-empty, then [[ -z "$VAR" ]] is false (returns 1) and the then statement does not execute.

Did you intend for the test to return true if the variable was non-empty? If so, replace -z with -n:

$ var=""; [[ -n "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ -n "$var" ]]; echo $?

0

For brevity, the same test is performed if -n is omitted:

$ var=""; [[ "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ "$var" ]]; echo $?

0

share|improve this answer

edited 1 hour ago

answered 1 hour ago

John1024John1024

48.4k5113128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I just posted my real code. I cannot, for the life of me, get that to work. I'm literally going fucking nuts.
  
  – StevieD
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @StevieD Run set -x and then run your code. This will show you how every step is evaluated.
  
  – John1024
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Ah, shit. Forgot about that setting. I'll try it.
  
  – StevieD
  1 hour ago
  

  
  
  
  

add a comment | 

The key is that 0 means true and 1 (or any other non-zero value) means false.

In shell, a test that is true (or a program which completes successfully), exits with code 0. The test [[ -z "$VAR" ]] returns code zero (true) if $VAR is empty or one (false) if it is not empty:

$ var=""; [[ -z "$var" ]]; echo $?

0

$ var="NOT EMPTY"; [[ -z "$var" ]]; echo $?

1

In sum, if $VAR is non-empty, then [[ -z "$VAR" ]] is false (returns 1) and the then statement does not execute.

Did you intend for the test to return true if the variable was non-empty? If so, replace -z with -n:

$ var=""; [[ -n "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ -n "$var" ]]; echo $?

0

For brevity, the same test is performed if -n is omitted:

$ var=""; [[ "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ "$var" ]]; echo $?

0

share|improve this answer

edited 1 hour ago

answered 1 hour ago

John1024John1024

48.4k5113128

$ var=""; [[ -z "$var" ]]; echo $?

0

$ var="NOT EMPTY"; [[ -z "$var" ]]; echo $?

1

$ var=""; [[ -n "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ -n "$var" ]]; echo $?

0

$ var=""; [[ "$var" ]]; echo $?

1

$ var="NOT EMPTY"; [[ "$var" ]]; echo $?

0

share|improve this answer

edited 1 hour ago

answered 1 hour ago

John1024John1024

48.4k5113128

answered 1 hour ago

John1024John1024

48.4k5113128

answered 1 hour ago

John1024John1024

48.4k5113128